eis: Add API to add client getting an fd

Creates the socket and adds it; is intended to be used to create client
connections that are passed via a secure channel, e.g. via portals.

Signed-off-by: Jonas Ådahl <jadahl@gmail.com>

src/libeis-fd.c

@@ -86,3 +86,24 @@ eis_backend_fd_add_fd(struct eis *eis, int fd)
 
 	return 0;
 }
+
+_public_ int
+eis_backend_fd_add_client(struct eis *eis)
+{
+	assert(eis);
+	assert(eis->backend);
+
+	int fds[2];
+
+	int rc = socketpair(AF_UNIX, SOCK_STREAM|SOCK_NONBLOCK|SOCK_CLOEXEC, 0, fds);
+	if (rc == -1)
+		return -errno;
+
+	struct eis_client *client = eis_client_new(eis, fds[0]);
+	if (client == NULL)
+		return -ENOMEM;
+
+	eis_client_unref(client);
+
+	return fds[1];
+}

src/libeis.h

@@ -403,11 +403,20 @@ int
 eis_setup_backend_fd(struct eis *ctx);
 
 /**
- * Add a new client to a context set up with eis_setup_backend_fd()
+ * Add a new client given a file descriptor to a context set up with
+ * eis_setup_backend_fd()
  */
 int
 eis_backend_fd_add_fd(struct eis *ctx, int fd);
 
+/**
+ * Add a new client to a context set up with eis_setup_backend_fd(). Returns
+ * a file descriptor to be passed to ei_setup_backend_fd(), or a negative
+ * errno on failure.
+ */
+int
+eis_backend_fd_add_client(struct eis *ctx);
+
 /**
  * libeis keeps a single file descriptor for all events. This fd should be
  * monitored for events by the caller's mainloop, e.g. using select(). When